The present invention relates to a device for applying laser radiation to an at least partially reflective or transparent area of a workpiece disposed in a work area according to the preamble of the claim 1 The present invention further relates to a device for reproducing a linear light distribution according to the preamble of claim 14, a laser device having such a device and a method for producing such a device.
Definitions: “In the direction of propagation of the laser radiation” refers to the average propagation direction of the laser radiation, in particular when the laser radiation is not a plane wave, or is at least partly divergent. Laser beam, light beam, sub-beam or beam, if not explicitly stated otherwise, does not refer to an idealized beam of geometrical optics, but a real light beam, such as for example a laser beam having a Gaussian profile, or a modified Gaussian profile or a top-hat profile, having not an infinitesimally small, but rather an extended beam cross section. Focal length of a lens or a cylindrical lens refers to the focal length of the lens in vacuum (refractive index nv=1).
It should also be noted at this point that the refractive index in a medium—for example in air or glass—depends on the wavelength of light to be refracted. The refractive index is therefore designated hereinafter with n(λ). An introduction to the theory of such dependencies can be found, for example, in Born, Max and Wolf, Emil, “Principles of Optics”, 7th edition, Cambridge University Press, Cambridge, 1999, pp. 97 ff.
Devices for applying laser radiation of the aforementioned type are well known. For example, the laser radiation is focused in a work area by a focusing lens, in which for example a layer of a substrate to which the laser radiation is to be applied in order cause to a chemical reaction or a structural transformation, and the like.
However, the prior art devices are not very effective when this layer has only a low optical density at the wavelength of the laser radiation, because in this case only a small fraction of the laser radiation is absorbed by the layer.
A device for reproducing a linear light distribution of the aforedescribed type is known, for example, from DE 199 36 230 A1. There, four arrays of cylindrical lenses are arranged in succession on two substrates in the propagation direction of the light of a light distribution to be imaged, wherein both the entrance surface and the exit surface of each of the substrates is provided with one of the arrays. All the cylindrical lenses are identical and have the same focal length. The thickness of the substrates and hence the distances between the array on the entrance side and the exit side each correspond to twice the focal length of the cylindrical lenses in the material of the substrates or to the product of twice the focal length and the refractive index of the material. The successively arranged cylindrical lenses then operate as a double telescope, so that the light distributions arranged at twice the focal length of the cylindrical lenses in front of substrates are imaged with a ratio 1:1 onto a plane disposed behind the substrates at a distance of twice the focal length.
Disadvantageously, such arrangement enables, on one hand, only size-preserving reproducing when the light distribution to be imaged is arranged in front of the substrates at twice the focal length of the cylindrical lenses. Furthermore, light beams incident at a large angle relative to the normal cannot realistically contribute to the image. In particular, such conventional device is unable to satisfactorily image a linear light distribution with a substantial longitudinal extent of, for example, more than 1 m in the direction of the line.